1. Field of the Invention
The present invention relates generally to the type of refrigerated display case commonly known as a "reach-in" case used in food stores and commonly having a glass door through which access is had to a product display space. In a more particular sense the invention relates to cases of this type in which the primary source of defrost heat is ambient air introduced into the case to flow through the evaporator. Thus, the case may be regarded as falling within the field of those in which the means for preventing or handling atmospheric condensate relative to the heat absorber means incorporated in the case, is a fluid--in particular, air--drawn from the surrounding ambient atmosphere.
Further with regard to the field of the invention, the introduction of the ambient air into a display case of the type having spaced, elongated air inlets and outlets providing an air curtain within the case that extends continuously about the product display area thereof, albeit with the added provision of a closed door that prevents impingement of ambient air upon the air curtain, is disclosed.
2. Description of the Prior Art
It is common to provide a reach-in display case with air defrost means adapted to introduce ambient air into the case for passage through the evaporator coil. The use of air defrost, as compared to electrical or hot gas defrost arrangements, has in recent years gained in popularity. It has been considered, for example, that air defrost may have advantages over defrost systems in which electrical resistance elements are the primary defrosters. In such instances, a considerable reduction in the expenditure of electrical energy may be anticipated. And, air defrost is preferred by some over "hot gas" defrost, by reason of its simplicity when compared against the additional piping, valving, and pressure controls required in the typical hot gas defrost system.
In reach-in, closed-door display cases of the air curtain type, it has been proposed to utilize ambient air for defrost purposes primarily by the operation of inlet and discharge dampers. These dampers, normally closed during refrigeration, are typically moved to open positions for communicating at least a part of the primary air passage with ambient at opposite sides of the coil. See, for example, U.S. Pat. No. 4,072,488 to Johnston issued Feb. 7, 1978; and U.S. Pat. No. 4,242,882 to Abraham issued Jan. 6, 1981.
Certain deficiencies have been noted in the prior art as typified by the above identified patents. It is believed desirable, for example, to provide a defrost system which will interfere minimally with the smooth flow of air during refrigerating cycles; that is to say, the air defrost system should not require baffling or restrictions that are aids during the defrost cycle, but which unfortunately remain present during refrigerating cycles to an extent that it inhibits the smooth, uniform flow of refrigerated air. Further, it is equally desirable to avoid relatively expensive components such as reversible primary fans, which are not only more expensive, but which in many instances do not operate in the reverse direction with the same efficiency as in their normal, forward direction.
In systems of this type, the incorporation of an air defrost arrangement is a trade-off in which, to gain the benefits of using ambient air as the heat source for defrosting a coil, it is necessary to accept a lower operating efficiency during refrigeration, or the incorporation of expensive components, or both. The present invention seeks to improve generally over the prior art by offering an air defrost system which attains high efficiency during defrost cycles with minimal reduction of operating efficiency in the refrigerating mode, and doing this without using expensive, trouble-prone mechanisms or assemblies.